S9^ Geological Society, 



that the upper is characterized by a mixture of marine and fresh- 

 water shells, the freshwater genera being Cyrena, Neritina, Me- 

 lanopsis, and Planorbis. The lower division contains exclusively 

 marine shells. The author refers this intermixture to the in- 

 flux of a river into the sea, in which the London clay was formed. 

 Mr. Morris considers the Bognor strata, which rest immediately 

 upon chalk, as the equivalents of the lower Woolwich deposit, ob- 

 serving that the shells agree with those of the London clay. These 

 remarks seem to confirm the conclusion to which he had been pre- 

 viously led by the grand section at Alum Bay in the Isle of Wight, 

 namely, that the beds usually styled plastic and London clays be- 

 long to one zoological period. 



MINERAL VEINS. 



Your attention has been called to the origin of mineral veins by 

 Mr. Fox, who has endeavoured to explain why so large a propor- 

 tion of the metalliferous veins in England and other parts of the 

 world should have an east and west direction. He supposes fis- 

 sures filled with water, containing sulphurets and muriates of cop- 

 per, tin, iron, and zinc in solution, through which currents of voltaic 

 electricity are transmitted. The metals separated from their sol- 

 vents by this action are deposited in the veins, and most abundantly 

 in veins running at right angles to the direction of the earth's mag- 

 netism ; for as the magnetic currents of the earth pass from north 

 to south, they cause those of electricity to move east and west, al- 

 though considerable deviations from this direction must be occa- 

 sioned in the course of geological epochs by variations in the mag- 

 netic meridian*. 



Since Mr. Fox first ascertained the existence of electric currents 

 in some of the metalliferous veins in Cornwall-j-, Mr. Henwood has 

 made many experiments on the same subject, together with obser- 

 vations on the distribution of metallic and earthy minerals in veins. 

 He considers the results obtained by him to be in a great degree op- 

 posed to the theory of Mr. Fox J. 



Mr. Fox conceives the fissures in which metalliferous substances 

 occur, to have been at firstsmall and narrow, and to have increased gra- 

 dually in their dimensions. This doctrine has also been propounded 

 in a work with which you are probably familiar, and from which I 

 have derived much instruction, 1 mean M. Fournet's Essay on Me- 

 talliferous Deposits. This Essay was originally included in the 3rd 

 volume of M. Burat's continuation of D'Aubuisson's Treatise on 

 Geology (1835), but it is now published separately, and gives the 

 clearest general view which I have seen of the application of geo- 

 logical theories to phaenomena observed in mining. It is written 



• [Mr. Fox's paper was noticed in Lond. and Edinb. Phil. Mag., vol. ix. 

 p. 387.— Edit.] 



t Phil. Trans. 1830, p. 399. 



X See Mining Journal,. Supplement 9. p. 34, December 1836, and Annals 

 of Electricity, No. 2. vol. i. on Electric Currents, &c. by W. T. Henwood, 

 Esq. 



